Handles for electronic screwdrivers and the like conventionally are slim and have a small diameter to permit delicate work when tightening and loosening very small screws. Such handles typically are provided with a rotating cap having a dome-shaped recess in the end face of the cap for use in centering the hand tool between the fingertip and the working tip of the screwdriver.
Generally, only one handle size is provided for slotted screws having a contemplated range of blade edge widths of 0.8 to 4 mm., a range whose test moment of torsion ratio is approximately 1:20. Such known handles typically are made completely of a hard synthetic plastic material, or, particularly in conjunction with newer handle designs, are made of a basic body of hard synthetic plastic material whose surface is partially covered with a soft synthetic material. Handles made of hard synthetic material that do not have a surface of soft synthetic material do not meet the current requirements for an ergonomically correct tool handle design. Moreover, if the contour of the handle body is substantially derived from cylindrical or conical shapes, it will not meet current design requirements.
The prior art has provided different handles of this particular kind. One known handle consisting of two synthetic materials has a slightly convex contour over its total longitudinal extension up to the point where the handle body joins the rotatable end cap. This design does not differentiate between the contact area for the palm of the hand and that for the fingertips. For this reason, it is difficult to perform delicate work using the fingertips.
In another known handle consisting of two synthetic materials, the diameter is substantially very small over the entire length of the handle. At the front third, the handle is provided with an approximately barrel-shaped enlargement wherein soft synthetic material is provided in pockets in the handle distributed over the circumference of the handle. While one's fingers may find a good fit between the blade-side top of the handle and the barrel-shaped enlargement, the fit of the palm of the hand on the handle is inconvenient. Such good fit generally would be required for transferring somewhat higher moments of torsion, such as, for example, when tightening or loosening larger screws.
In light of these drawbacks of known electronic screwdrivers or handles for similar tools, there exists a need in the art for a more versatile handle for the special requirements of the application. It is a general object of the invention to design a handle of that kind, that generally gives a comfortable grip, and that provides a good support of the handle, both in the palm of the hand, and against the fingertips. The handle should permit centering between the working tip of the tool (such as a screwdriver tip) and the hand, and provide a sufficiently large, discontinuous area for imprinting of the handle. The handle should be able to accommodate primarily low-torque and medium-torque applications.